When diamond is chemically vapor deposited, large intrinsic tensile stresses are typically present. At the usual temperatures of CVD diamond deposition at 750 to 900 degrees Centigrade, diamond is a brittle material and will not plastically flow. As a result, these deposition stresses cannot relax. The presence of these stresses can be seen in polarized optical transmission microscopy. The initial layer of CVD diamond may relax some of this tensile stress by deforming the underlying substrate.
Increasing demands are being put on as-grown CVD diamond. For instance, windows must have the highest possible transmission of laser light. The presence of grain boundaries, defects, dislocations, plastic strain and other sources of density fluctuation within the diamond window reduce its transmission, increase its absorption of incident radiation and reduce its thermal conductivity, mechanical strength and mechanical toughness. Absorption of laser energy creates heat within the window which must be drained through the diamond body to an adjacent heat sink in contact with the diamond part. If heat dissipation is rate limiting, the temperature of the window will increase causing distortion of the window-fixture and failure of the entire window assembly.
Polycrystalline diamond films prepared by CVD methods suffer from visual and mechanical defects associated with grain boundaries and growth defects including voids. In addition, residual stresses associated with the growth processes may be undesirable. Subsequent use of CVD polycrystalline diamond films in tools, electro-optical applications, and so on may be inhibited by the presence of these defects. Hence, to improve the utilization of CVD diamond, it is desirable to enhance the desirable properties of the diamond by addressing the aforementioned problems.